A simulation study was done to investigate the effect of the coefficient of variation of the modulus of elasticity ((E) on the vibrational performance of joist floor systems. Eight floor cases were studied and two types of lumber were considered: MSR and VSR lumber where (E is 0.11 and 0.25, respectively. The expected floor vibrational performance of MSR versus VSR lumber floors was evaluated by: 1) the probability that the fundamental frequency is less than 10 Hz and 2) the ratio of the first percentile of predicted fundamental frequency of MSR to VSR lumber. / Master of Engineering